Bicycles are not available for rent inside the park  
If you plan to bring a bicycle, be aware that in Arizona, bicycles are subject to the same traffic rules as automobiles. Use extreme caution when riding on park roads! Shoulders are narrow and vehicle traffic is heavy.

Bicycles Sites are available in the park's campgrounds
The bicycle/backpack sites at Mather Campground (S. Rim) and at the North Rim Campground, are shared sites. Bicycle/backpack sites are $6.00 per person, per night. NO CARS ALLOWED!

All park shuttle buses are equipped with bicycle racks
Bicycle one way and ride the shuttle the other.

Bicycles are prohibited
On all other trails, inside the canyon, and also including the Rim Trail. Bicyclists must obey all traffic regulations. Always ride single file with the flow of traffic. See and be seen; wear bright colors and a helmet.

Bicycles are permitted
On all paved and unpaved park roads and the new 2.8 mile / 4.5 km Hermit Road Greenway Trail (South Rim.) 

On the Hermit Road, bicyclists should pull to the right shoulder and dismount when large vehicles are attempting to pass. Never hang onto a shuttle bus while riding. The new Hermit Road Greenway Trail segment, between The Abyss and Hermit Rest, provides a bicycle path away from the road.

Hermit Road Greenway Trail (2008)